1. Cross-Reference to Related Application
Reference is directed to commonly assigned co-pending U.S. patent application Ser. No. 07/958,019 filed on even data herewith in the names of Ronald G. Rosene, Richard L. Timp, and John H. Morehead, and entitled LOCKING RING STRIPPER PLATE ASSEMBLY.
2. Technical Field
The invention relates generally to punch set assemblies used in punch presses, and particularly to adjustable length punch set assemblies wherein the punch may be adjusted to compensate for punch blade length reduction due to sharpening.
3. Description of the Prior Art
Repeated use of a punch assembly in a punch press operation results in the natural dulling and wear of the punch blade or tip. Once the tip has become dull, the effectiveness of the punch assembly is reduced and the punch tip must be sharpened. Sharpening may be accomplished by grinding the end of the punch tip, and this results in shortening the length of the blade and, consequently, the punch. The length of the punch then must be adjusted to compensate for the ground-off portion of the punch blade.
A first type of punch set assemblies that allow for length corrections are exemplified in U.S. Pat. Nos. 4,031,787 and 4,141,264. These patents disclose punch sets that compensate for the shortened punch blade length by adding shims, washers or other similar objects to the punch. The problem with this method is that the added washers or the like are usually weak and cannot withstand the constant cyclical forces placed upon a punch. Also, the length of the punch tip can only be adjusted within certain limits before it becomes too short for effective operation, thereby limiting the number of times the punch tip can be sharpened. In addition, most such methods that allow for the adjustment of the length of the punch tip require dismantling of the entire punch in order to access the punch tip for adjustment; this obviously can be a rather time-consuming process. Additionally, once the punch has been reassembled, further effort is frequently expended in determining how much the sharpening and adjusting steps have affected the axial position of the tip with reference to the plane of the stripper plate opening that it extends through in use.
Improvements on these known methods are described in commonly assigned U.S. Pat. No. 4,375,774 and in co-pending U.S. patent application Ser. No. 743,689 filed Aug. 12, 1992, now U.S. Pat. No. 5,131,303. In the '774 patent and the '689 application, the punch driver and punch holder or body components of the punch are attached by mutually engageable threaded portions so that overall punch length adjustment may be accomplished by rotation of the threaded portions so that the punch tip may be properly aligned with the opening in the stripper plate. Locking mechanisms are provided in each case. In the '774 patent, an expandable locking pin is inserted into aligned locking pin holes wherein it interferes with and prevents rotation of the threaded portions. While simplifying the axial length adjustment process, this approach requires removal and re-insertion of the locking pin.
In the '689 application, the assembled punch is axially slidably received within a bore provided in a punch guide. A releasable lock for locking the threaded ends against relative rotation is provided by an arcuate wire clip having a radially inwardly extending cam pin. The arcuate clip is retained in an annular groove and radially inwardly extending bore in the punch holder so that the cam pin extends inwardly and into engagement with a set of circumferentially distributed grooves in the male threaded end of the punch body. Length adjustment in either direction is provided by rotating the punch body with respect to the punch holder so that the cam tip is released from one groove and engages a further groove. Such adjustable length punch sets are useful for relatively small diameter punch sets.
An adjustable length forming tool head is disclosed in U.S. Pat. No. 5,020,407 which discloses a length adjustment in the threaded connection between the punch driver and the punch head base which in turn is attached to a form tool body. A length control ring member is spring biased away from and between the driver and the base and is formed with a central opening for engaging the shaft of the driver to prevent their relative rotation and a set of circumferentially spaced apertures for engaging a pair of pins extending from the base. Adjustment is accomplished by grasping the ring member and driver to withdraw the ring member from engagement with the pins and to rotate them until the next desired set of diametrically opposed apertures is aligned with the pins. Since the form tool does not have a punch set spring encircling the punch head, it is possible to grasp the ring member and make the length adjustment. Such an arrangement would not be useable in punch sets having a punch spring encircling the punch head, driver and holder components of the type disclosed in the above referenced patents and application.
A need exists, therefore, for an accurate means of adjusting the length of the punch in a manner that is not overly time consuming or difficult.